Liquid or semi-solid formulations containing one or more polypeptides are typically subject to degradation during storage, such as due to oxidation. It has been found to be difficult or even impossible to prepare and package a peptide-containing formulation so as to guarantee that oxidants, atmospheric oxygen and formulation excipients bearing residual oxidants, will be excluded. Oxygen and residual oxidants cause rapid oxidation of many of the amino acid residues in a polypeptide.
Methionine is an amino acid residue that is vulnerable to oxidation. In the presence of oxidants, methionine is rapidly oxidized to methionine sulfoxide. Takruri, U.S. Pat. No. 5,272,135 discloses that adding methionine to a liquid or semi-solid medium containing a methionine-containing polypeptide is effective to inhibit the oxidation of methionine residues in the polypeptide to methionine sulfoxide. According to the method of Takruri, methionine is added to a pharmaceutical preparation comprising a methionine-containing polypeptide in a quantity sufficient to inhibit the oxidation of methionine residues to methionine sulfoxide.
Many pharmaceutically active polypeptides exist that lack methionine residues. An example of one such polypeptide is P-113, a 12-amino acid polypeptide fragment of histatin 5 that has antimicrobial activity against Candida spp. and that has been used topically to treat atopic dermatitis. See, Rothstein, et al, Antimicrobial Agents and Chemotherapy, 45(5):1367-1373 (2001). As disclosed in Rothstein, the P-113 polypeptide has an amino acid sequence that lacks methionine.
Methionine-free polypeptides such as P-113 often contain amino acids that are subject to oxidation and, therefore, although these polypeptides lack methionine, they also tend to degrade in the presence of oxygen. A substantial need exists for a method to stabilize polypeptides in liquid or semi-solid pharmaceutical formulations wherein the polypeptides have an amino acid sequence that is free of methionine.